InSAR measurements of compaction and subsidence in the Ganges‐Brahmaputra Delta, Bangladesh

Abstract

Many of the world′s largest river deltas are sinking due to sediment loading, compaction, and tectonics but also recently because of groundwater extraction, hydrocarbon extraction, and reduced aggradation. Little is known, however, about the full spatial variability of subsidence rates in complex delta systems. This study reconstructs subsidence rates in the eastern portion of the Ganges-Brahmaputra Delta (GBD), Bangladesh, covering more than 10,000 km 2 at a high spatial resolution of 100 m. The map was produced using Interferometric Synthetic Aperture Radar (InSAR) covering the period 2007 to 2011. Eighteen Advanced Land Observing Satellite Phased-Array L-band SAR scenes were used to generate 30 interferograms calibrated with GPS. Interferograms were stacked to yield average subsidence rates over the study period. Small Baseline Subset-InSAR was then applied to validate the results against an additional GPS record from Dhaka, Bangladesh. Land subsidence of 0 to > 10 mm/yr is seen in Dhaka, with variability likely related to local variations in shallow subsurface sediment properties. Outside of the city, rates vary from 0 to > 18 mm/yr, with the lowest rates appearing primarily in Pleistocene Madhupur Clay and the highest rates in Holocene organic-rich muds. Results demonstrate that subsidence in this delta is primarily controlled by local stratigraphy, with rates varying by more than an order of magnitude depending on lithology. The ability of L-band InSAR to differentiate between stratigraphic units in this humid, vegetated subtropical river delta demonstrates the power of interferometry as a tool for studying the subsurface in deltaic environments.

Detailed quantification of delta subsidence, compaction and interaction with man-made structures: the case of the NCA airport, France

“…4e). These CR values are in the range of what it is observed for modern deltas: 1-2 mm yr −1 for the Fraser, Nile and Mississippi deltas (Mazzotti et al, 2009;Wöppelmann et al, 2013;Törnqvist et al, 2008) and up to 15-18 mm yr −1 in some parts of the Po and Ganges-Brahmaputra deltas (Teatini et al, 2011;Higgins et al, 2014). Contrary to those studies (except for the Po delta that seems to behave similarly), the CR increases until the coastline.…”

“…Indeed, many of the world's largest river deltas are primarily sinking under the effect of sediment compaction (Syvitski et al, 2009). Examples include the Fraser river delta in Western Canada (Mazzotti et al, 2009), the Mississippi delta in the USA (Törnqvist et al, 2008), the Po delta in Italy (Teatini et al, 2011) or the Ganges-Brahmaputra delta in Bangladesh (Higgins et al, 2014).…”

Doomed to drown? Sediment dynamics in the human-controlled floodplains of the active Bengal Delta

“…Sediment accumulation in this poldered area also offsets regional, yet locally heterogeneous, subsidence rates of up to 1.8 cm yr -1 (c.f., Higgins et al, 2014;Brown and Nicholls, 2015). If our sedimentation results are considered alongside relative sea level rise and subsidence rates independently, and 2012 is assumed to represent an average flood year, it appears that mean annual accumulation is more than sufficient for reducing the risk of coastal flooding in the central lower Bengal Delta.…”

Modelling the increased frequency of extreme sea levels in the Ganges–Brahmaputra–Meghna delta due to sea level rise and other effects of climate change

“…These values are due to climate change alone, but subsidence will increase the rise in sea level experienced on the ground; this issue was raised by Milliman et a.l. 1 in 1989, when little data was available to quantify the effect, and studies since 2000 have confirmed that the coastal areas of the GBM delta are undergoing land subsidence 5,6 . Syvitski et al 7 argued that the entire GBM delta is sinking at an alarming rate.…”